This invention relates to a novel, modified, urethane polymeric system, eminently suited for the manufacture of foamed insulating products, especially so-called rigid, foamed insulating products.
Polyurethanes contain carbamate groups, --NHCOO--, also referred to as urethane groups in their backbone structure. Characteristically, they are obtained by the reaction of a diisocyanate with a macroglycol, sometimes more simply referred to as a polyol, or with a macroglycol and a short-chain glycol extender. The macroglycols or polyols are based on polyethers, polyesters, or a combination of both.
The polymerization of diisocyanates with macroglycols to produce urethane polymers was pioneered by O. Bayer. The polymerization process is frequently referred to as a polyaddition one, although there is some authority that it may also be referred to as partly condensation in nature. In any event, the urethane forming reaction is a rapid one, and high molecular weight polymers have been obtained from liquid monomers, even at ambient temperatures, to give products ranging from cross-linked network polymers to linear fibers and elastomers.
In addition to linear thermoplastic polymers, i.e., polyurethanes obtained from difunctional monomers, branched or crosslinked thermoset polymers are made with higher functional monomers. The higher functionality is obtained with higher functional isocyanates, typically so-called polymeric isocyanates, or with higher functional polyols.
Urethane network polymers may be formed by the trimerization of part of the isocyanate groups. The approach is frequently used in the formation of rigid-modified isocyanurate foams with the following structure: ##STR1##
Involved in the present invention herein are resin systems which have previously been investigated, but which have not, to the best of applicant's knowledge, ever been combined or "put together", so to speak, in the fashion or manner hereinafter disclosed.
Two basic independent formation reactions take place in my system, with a third one being optional. One involves the formation of the urethane polymer, and more specifically, involves the reaction of an isocyanate with a component containing hydroxyl groups. Utilizing bi- or polyfunctional polyols or compounds containing a multiplicity of hydroxyl groups, such as polyethers or polyesters, and di- or polyisocyanates, either linear or cross-linked polyurethanes are formed, depending upon the functionality of the reactants: This is an exothermic reaction and is shown generally as follows: ##STR2##
The properties, both physical and chemical, of the polymer depend upon the nature, functionalities and ratios of the reactants, all of which can be varied.
Polyesters which are hydroxy terminated are most often used with the isocyanates; glycols frequently used include, ethylene, propylene, butylene and diethylene; triols such as glycerol and trimethylol ethane and propane have also been used. Both saturated and unsaturated dicarboxylic polyesters have been used, including mixtures thereof.
In the systems involved in my invention, the polyester is an unsaturated polyester, or mixture thereof with a saturated polyester, but the unsaturated polyester forms the predominant entity. Thus, a second and independent reaction involved is the curing or cross-linking of the unsaturated polyester moiety with a cross-linking type of vinylidene monomer, for example, styrene, in the presence of a free radical catalyst. The unsaturated, polyester cross-linking reaction is shown generally, as follows: ##STR3##
Optionally, and when so desired, a third reaction can take place. When so desired, a conventional trimerization catalyst can be used to trimerize the isocyanate to produce polyisocyanate products. This is another exothermic reaction and is shown generally, as follows ##STR4##
The present invention carries out or controls these essentially independent reactions, in a surprising and unexpected manner, by mixing and reacting primarily only two reactant compositions or streams, each of which is so formulated, so that not only are the reactions initiated at substantially the same time, but that they (i.e., both independent reactions) proceed substantially uniformly and evenly, and within essentially the same time frame (total), from start to finish, that is to completition. This gives a product, especially a foamed product, with which the invention is primarily concerned, which is essentially homogeneous, and which has unexpectedly improved physical properties, especially the important physical property of dimensional stability.
With reference to specific prior art, worthy of mention is Graham et al., U.S. Pat. No. 3,860,537, which utilizes a stepwise procedure and partially cured precursors. Separate and distinct sequential polymerizations appear to be involved, a procedure which is inherently different than the procedure used in my invention. Foamed products are mentioned in Graham et al., and a polyol, an unsaturated polyester and isocyanate are used in Graham et al.
Another teaching in the field is that of Hutchinson et al, U.S. Pat. No. 3,886,229. While foams are not specifically mentioned, again precursors of the polymers are used in a manner different from that disclosed and claimed in my invention.
A more recent teaching in the prior art is that of Peterson et al, U.S. Pat. No. 4,386,166, which involves a foam prepared from an unsaturated polyester resin, a copolymerization monomer, a low molecular weight polyol and an isocyanate. As will become more apparent from the disclosure following hereinafter, my system and procedure involve several essential and unobvious differences from Peterson et al. For the present, however, it may be relevant to point out that the primary objectives in Peterson et al, are different from those in my invention; Peterson et al, apparently being primarily concerned with the manufacture of an insulating foam board, based on an unsaturated polyester resin, which is capable of high filler loadings and improved flame spread and smoke generation characteristics; said objectives in Peterson et al, are consistent inasmuch as it is known that certain fillers, such as hydrated alumina, the main filler used in Peterson et al, will improve flame retardant characteristics of polymeric foamed systems; whereas as stated before, I am primarily concerned with improving the physical dimensional stability of the foamed product, without any appreciable loss in the performance characteristics of other important properties.